Pneumatic Tire

ABSTRACT

In a pneumatic tire, a groove depth H1 of each of first and second inclined lug grooves over an entire region from an opening portion to a corresponding one of first or second circumferential main grooves to a terminating end portion within a center land portion has a relationship with a maximum groove depth Hg of the corresponding one of the first or second circumferential main grooves represented by 0.80≤H1/Hg≤1.00. Additionally, a maximum groove depth H2 of each of first and second lateral grooves has a relationship with a groove depth H1e at a terminating end portion of the corresponding one of the first and second inclined lug grooves represented by 0.70≤H2/H1e≤0.90.

RELATED APPLICATION

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2019-121682, filed Jun. 28, 2019, theentire contents of which is incorporated herein by reference.

TECHNICAL FIELD

The technology relates to a pneumatic tire and particularly relates to apneumatic tire that can provide improved mud performance of the tire.

BACKGROUND ART

Known off-road tires include a plurality of inclined lug grooves formedon a tread surface and each having a groove depth equivalent to that ofa main groove, in order to ensure appropriate traction characteristicswhile driving on a mud road. The technology described in JapanUnexamined Patent Publication No. 2015-227114 is a conventionalpneumatic tire that is configured in this manner.

SUMMARY

The technology provides a pneumatic tire that can provide improved mudperformance of the tire.

A pneumatic tire according to an embodiment of the technologycorresponds to a pneumatic tire including: first and secondcircumferential main grooves extending in a tire circumferentialdirection; and a pair of shoulder land portions and one row of a centerland portion defined by the first and second circumferential maingrooves,

the center land portion comprising: a first inclined lug grooveextending at an incline with respect to the tire circumferentialdirection and opening, at one end portion, to the first circumferentialmain groove and terminating, at another end portion, within the centerland portion; a second inclined lug groove extending at an incline in adirection identical to a direction of the first inclined lug groove andopening, at one end portion, to the second circumferential main grooveand terminating, at another end portion, within the center land portion;a first lateral groove connecting the first inclined lug groove with thesecond circumferential main groove; a second lateral groove connectingthe second inclined lug groove with the first circumferential maingroove; first and second auxiliary grooves connecting the first inclinedlug groove with the second inclined lug groove adjacent to each other;and a plurality of center block defined by the grooves,

a groove depth H1 of the first inclined lug groove over an entire regionfrom an opening portion to the first circumferential main groove to aterminating end portion within the center land portion having arelationship with a maximum groove depth Hg of the first circumferentialmain groove represented by 0.80≤H1/Hg≤1.00, and

a maximum groove depth H2 of the first lateral groove having arelationship with a groove depth H1e at the terminating end portion ofthe first inclined lug groove represented by 0.70≤H2/H1e≤0.90.

In the pneumatic tire according to the technology, (1) the inclined luggroove terminates within the center land portion without extendingthrough the center land portion. Thus, compared to a configuration inwhich the inclined lug groove extends through the center land portion,this configuration provides an increased mud column shear force duringtraveling on a mud road. This has the advantage of improving thetraction characteristics of the tire, improving the mud performance thetire. Additionally, (2) the maximum groove depth H2 of the lateralgroove is shallower than the groove depth H1e of the terminating endportion of the inclined lug groove, thus producing an effect that holdsback a flow path (that is, the lateral groove) from the inclined luggroove to the circumferential main groove. Thus, advantageously, theterminating end portion of the inclined lug groove has an increased soilcolumn shear force, further improving the mud performance of the tire.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view in a tire meridian directionillustrating a pneumatic tire according to an embodiment of thetechnology.

FIG. 2 is a plan view illustrating a tread surface of the pneumatic tireillustrated in FIG. 1.

FIG. 3 is an enlarged view illustrating a center land portionillustrated in FIG. 2.

FIG. 4 is a cross-sectional view of the center land portion taken alongline X-X in FIG. 3.

FIG. 5 is an explanatory diagram illustrating first center blocks of thecenter land portion illustrated in FIG. 3.

FIG. 6 is an explanatory diagram illustrating second center blocks ofthe center land portion illustrated in FIG. 3.

FIG. 7 is an enlarged view illustrating a notch portion illustrated inFIG. 5.

FIGS. 8A-8C include a table showing the results of performance tests ofpneumatic tires according to embodiments of the technology.

DETAILED DESCRIPTION

Embodiments of the technology are described in detail below withreference to the drawings. However, the technology is not limited tothese embodiments. Moreover, constituents of the embodiments includeelements that are substitutable while maintaining consistency with thetechnology, and obviously substitutable elements. Furthermore, themodified examples described in the embodiments can be combined asdesired within the scope apparent to one skilled in the art.

Pneumatic Tire

FIG. 1 is a cross-sectional view in a tire meridian directionillustrating a pneumatic tire according to an embodiment of thetechnology. The same drawing illustrates a cross-sectional view of ahalf region in a tire radial direction. Additionally, the same drawingillustrates a radial tire for a light truck as an example of a pneumatictire.

In reference to the same drawing, a cross-section in a tire meridiandirection is defined as a cross-section of the tire taken along a planethat includes a tire rotation axis (not illustrated). Additionally, atire equatorial plane CL is defined as a plane extending perpendicularlyto the tire rotation axis through the midpoint of measurement points ofa tire cross-sectional width defined by JATMA. Additionally, a tirelateral direction is defined as the direction parallel with the tirerotation axis. The tire radial direction is defined as the directionperpendicular to the tire rotation axis.

A pneumatic tire 1 has an annular structure with the tire rotation axisas its center and includes a pair of bead cores 11, 11, a pair of beadfillers 12, 12, a carcass layer 13, a belt layer 14, a tread rubber 15,a pair of sidewall rubbers 16, 16, and a pair of rim cushion rubbers 17,17 (see FIG. 1).

The pair of bead cores 11, 11 are formed by winding one or a pluralityof bead wires made of steel in an annular shape and in multiple layersand are embedded in respective bead portions to form cores of the leftand right bead portions. The pair of bead fillers 12, 12 are disposedoutward of the pair of bead cores 11, 11 in the tire radial directionand reinforce the bead portions.

The carcass layer 13 has a single layer structure made of one carcassply or a multilayer structure made of a plurality of carcass plies andextends between the left and right bead cores 11, 11 in a toroidalshape, forming the framework of the tire. Additionally, both endportions of the carcass layer 13 are turned back outward in the tirelateral direction so as to wrap around the bead cores 11 and the beadfillers 12 and fixed. Additionally, carcass plies in the carcass layer13 are made by performing a rolling process on coating rubber-coveredcarcass cords made of steel or an organic fiber material (e.g. aramid,nylon, polyester, rayon, or the like). Each of the carcass plies has acord angle (defined as the inclination angle, in the longitudinaldirection, of the carcass cords with respect to the tire circumferentialdirection) of 80 deg. or more and 100 deg. or less.

The belt layer 14 is a multilayer structure including a plurality ofbelt plies 141 to 143 and is disposed by being wound around the outercircumference of the carcass layer 13. The belt plies 141 to 143 includea pair of cross belts 141, 142 and a belt cover 143.

The pair of cross belts 141, 142 are made by performing a rollingprocess on coating rubber-covered belt cords made of steel or an organicfiber material. Each of the cross belts 141, 142 has a cord angle of 15deg. or more and 55 deg. or less as absolute values. Additionally, thepair of cross belts 141, 142 have cord angles (defined as inclinationangles, in the longitudinal direction, of the belt cords with respect tothe tire circumferential direction) of opposite signs and are layeredsuch that the longitudinal directions the belt cords intersect eachother (what is called a crossply structure). Additionally, the pair ofcross belts 141, 142 are disposed layered outward of the carcass layer13 in the tire radial direction.

The belt cover 143 is made by coating belt cover cords made of steel oran organic fiber material with coating rubber. The belt cover 143 has acord angle of 0 deg. or more and 10 deg. or less as absolute values.Additionally, the belt cover 143 is, for example, a strip materialformed by coating one or a plurality of belt cover cords with coatingrubber and winding the strip material spirally around the outercircumferential surface of the cross belts 141, 142 a plurality of timesin the tire circumferential direction. Additionally, the belt cover 143is disposed covering the entire areas of the cross belts 141, 142.

The tread rubber 15 is disposed outward of the carcass layer 13 and thebelt layer 14 in the tire radial direction and constitutes a treadportion. The pair of sidewall rubbers 16, 16 are disposed outward of thecarcass layer 13 in the tire lateral direction and constitute left andright sidewall portions. Each of the pair of rim cushion rubbers 17, 17extends, from an inner side of a corresponding one of the left and rightbead cores 11, 11 and a turned back portion of the carcass layer 13 inthe tire radial direction, outward in the tire width direction, forminga rim engaging surface of the bead portion.

Tread Pattern

FIG. 2 is a plan view illustrating a tread surface of the pneumatic tireillustrated in FIG. 1. The same drawing illustrates a tread surface ofan off-road tire. In reference to the same drawing, “tirecircumferential direction” refers to the direction revolving about thetire rotation axis. A reference sign T denotes a tire ground contactedge, and a dimensional sign TW denotes a tire ground contact width.

As illustrated in FIG. 2, the pneumatic tire 1 includes, in a treadsurface, a pair of circumferential main grooves 2A, 2B; and a pair ofshoulder land portions 31A, 31B and one row of a center land portion 32defined by the circumferential main grooves 2A, 2B.

Each of the circumferential main grooves 2A, 2B has a zigzag shape withan amplitude in the tire lateral direction. Additionally, each of thecircumferential main grooves 2A, 2B is obliged to include a wearindicator specified by JATMA (The Japan Automobile Tyre ManufacturersAssociation, Inc.) and typically has a groove width of 7.0 mm or moreand a groove depth of 8.5 mm or more.

The groove width is measured as a distance between opposing groove wallsat a groove opening portion with the tire mounted on a specified rim andinflated to a specified internal pressure and in an unloaded state. In aconfiguration including a notch portion or a chamfered portion at thegroove opening portion, the groove width is measured using, asmeasurement points, intersection points between an extension line of atread contact surface and extension line of the groove walls, in across-sectional view parallel to a groove width direction and a groovedepth direction.

The groove depth is measured as a distance from the tread contactsurface to a maximum groove depth position with the tire mounted on aspecified rim and inflated to the specified internal pressure and in anunloaded state. Additionally, in a configuration in which a partialrecess/protrusion portion and a sipe at the groove bottom, the groovedepth is measured by excluding these portions.

“Specified rim” refers to a “standard rim” defined by JATMA, a “DesignRim” defined by TRA (The Tire and Rim Association, Inc.), or a“Measuring Rim” defined by ETRTO (The European Tyre and Rim TechnicalOrganisation). Additionally, “specified internal pressure” refers to a“maximum air pressure” defined by JATMA, the maximum value in “TIRE LOADLIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, or“INFLATION PRESSURES” defined by ETRTO. Additionally, “specified load”refers to a “maximum load capacity” defined by JATMA, the maximum valuein “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined byTRA, or “LOAD CAPACITY” defined by ETRTO. However, in JATMA, for apassenger vehicle tire, the specified internal pressure is an airpressure of 180 kPa, and the specified load is 88% of the maximum loadcapacity at the specified internal pressure.

Additionally, in the configuration in FIG. 2, the pneumatic tire 1 has asubstantially point-symmetric tread pattern with a center point on thetire equatorial plane CL. However, no such limitation is intended, andthe pneumatic tire 1 may have a point-asymmetric tread pattern (notillustrated).

Additionally, in FIG. 2, a maximum ground contact width Wb1 of each ofthe shoulder land portion 31A, 31B with respect to the tire groundcontact width TW is preferably in the range of 0.50≤Wb1/TW≤0.80 and morepreferably in the range of 0.55≤Wb1/TW≤0.70.

Additionally, a maximum ground contact width Wb2 of the center landportion 32 with respect to the tire ground contact width TW ispreferably in the range of 0.30≤Wb2/TW≤0.60 and more preferably in therange of 0.40≤Wb2/TW≤0.50.

The ground contact width of a land portion is measured as a lineardistance in the tire axial direction on a contact surface between theland portion and a flat plate, with the tire mounted on a specified rim,inflated to the specified internal pressure, and placed perpendicularlyto the flat plate in a stationary state and loaded with a loadcorresponding to the specified load.

The tire ground contact width TW is measured as a linear distance in thetire axial direction on a contact surface between the tire and a flatplate, with the tire mounted on a specified rim, inflated to thespecified internal pressure, and placed perpendicularly to the flatplate in a stationary state and loaded with a load corresponding to thespecified load.

The tire ground contact edge T is defined as the maximum width positionin the tire axial direction of the contact surface between the tire anda flat plate, with the tire mounted on a specified rim, inflated to thespecified internal pressure, and placed perpendicularly to the flatplate in a stationary state and added with a load corresponding to thespecified load.

Additionally, as illustrated in FIG. 2, the pair of shoulder landportions 31A, 31B and the center land portion 32 are disposedoverlapping each other as viewed in the tire circumferential direction.Accordingly, the circumferential main grooves 2A, 2B have asee-through-less structure as viewed in the tire circumferentialdirection.

Additionally, an overlapping amount Db between each of the shoulder landportions 31A, 31B and the center land portion 32 has a relationship withthe tire ground contact width TW represented by 0≤Db/TW≤0.10.

The overlapping amount Db of each of the land portions 31A, 31B, 32 ismeasured as a distance in the tire lateral direction between themeasurement points of the maximum ground contact widths Wb1, Wb2 of theland portion 31A, 31B, 32.

Shoulder Land Portions

As illustrated in FIG. 2, each of the shoulder land portions 31A, 31Bincludes a plurality of shoulder lug grooves 311 and a plurality ofshoulder blocks 312 defined by the shoulder lug grooves 311.

Each of the shoulder lug grooves 311 extends in the tire lateraldirection, opens, at one end portion, to the circumferential main groove2A, 2B, and opens, at the other end portion, to the tire ground contactedge T. Additionally, the plurality of the shoulder lug grooves 311 arearranged at predetermined intervals in the tire circumferentialdirection. In addition, each of the shoulder lug grooves 311 has agroove width of 13 mm or more and a groove depth of 8.0 mm or more. Thegroove depth of the shoulder lug groove 311 with respect to the groovedepth of the circumferential main groove 2A is in the range of 80% ormore and 100% or less. Additionally, in the configuration in FIG. 2, theshoulder lug grooves 311 are disposed, the number of which is the sameas the pitch number of the zigzag shape of the circumferential maingrooves 2A, and each of the shoulder lug grooves 311 opens at a maximumamplitude position of the circumferential main groove 2A, 2B outward inthe tire lateral direction.

The shoulder block 312 has a convex edge portion protruding toward thetire equatorial plane CL along the zigzag shape of the circumferentialmain groove 2A, 2B. Additionally, the plurality of shoulder blocks 312are arranged at predetermined intervals in the tire circumferentialdirection to form a single block row. Additionally, in the configurationof FIG. 2, the shoulder blocks 312 are formed, the number of which isthe same as the pitch number of the zigzag shape of the circumferentialmain grooves 2A. Additionally, each of the shoulder blocks 312 includes:a semi-closed lug groove (reference sign omitted in drawings) thatopens, at one end portion, to the tire ground contact edge T and thatterminates, at the other end portion, within the shoulder block 312, aplurality of sipes (reference sign omitted in drawings); and pin holes(reference sign is omitted in the drawings) into which studless pins areinserted.

Center Land Portion

FIG. 3 is an enlarged view illustrating the center land portionillustrated in FIG. 2. FIG. 4 is a cross-sectional view of the centerland portion taken along line X-X in FIG. 3.

As illustrated in FIG. 3, the center land portion 32 includes: first andsecond inclined lug grooves 321A, 321B; first and second lateral grooves322A, 322B; first and second auxiliary grooves 323A, 323B; and aplurality of center blocks 41A, 41B, 42A, 42B defined by the grooves.

As illustrated in FIG. 2, each of the first inclined lug grooves 321Aextends at an incline with respect to the tire circumferential directionand intersects the tire equatorial plane CL. Additionally, the firstinclined lug groove 321A opens, at one end portion, to the firstcircumferential main groove 2A and terminates, at the other end portion,within the center land portion 32. The each of second inclined luggrooves 321B extends at an incline in the same direction as the firstinclined lug grooves 321A and intersects the tire equatorial plane CL.Additionally, each of the second inclined lug grooves 321B opens, at oneend portion, to the second circumferential main groove 2B andterminates, at the other end portion, within the center land portion 32.Accordingly, the first and second inclined lug grooves 321A, 321B areinclined in the same direction with respect to the tire circumferentialdirection and open to the different circumferential main grooves 2A, 2B.

Additionally, each of the first and second inclined lug grooves 321A,321B has a groove width of 5.0 mm or more and a groove depth of 8.0 mmor more. In the configuration in FIG. 3, the first and second inclinedlug grooves 321A, 321B are main grooves and, as illustrated in FIG. 4,have substantially the same maximum groove depth as that of thecircumferential main grooves 2A, 2B. Specifically, a groove depth H1 ofthe inclined lug groove 321A, 321B over the entire area from the openingportion at the circumferential main groove 2A, 2B to the terminating endportion in the center land portion 32 has a relationship with a maximumgroove depth Hg of the circumferential main groove 2A, 2B represented by0.80≤H1/Hg≤1.00 and more preferably by 0.90≤H1/Hg≤1.00. Thus, each ofthe inclined lug grooves 321A, 321B is defined as a continuous grooveportion having the groove depth H1 described above, and the terminatingend portion is defined as the end portion of the above-described grooveportion in the center land portion 32.

In the configuration described above, each of the inclined lug grooves321A, 321B terminates within the center land portion 32 withoutextending through the center land portion 32. Thus, compared to aconfiguration in which the inclined lug groove extends through thecenter land portion (not illustrated), this configuration provides anincreased soil column shear force during traveling on a mud road. Thus,the traction characteristics of the tire are improved and the mudperformance of the tire is improved. Additionally, the rigidity of thecenter blocks 41A to 42B is increased to improve the wear resistanceperformance of the tire.

Additionally, in FIG. 3, an inclination angle θ1 of each of the firstand second inclined lug grooves 321A, 321B in the tire equatorial planeCL is preferably in the range of 25 deg.≤θ1≤70 deg. and more preferablyin the range of 30 deg.≤θ1≤50 deg.

The inclination angle θ1 of the inclined lug groove is measured as anangle between the groove center line of the inclined lug groove and thetire equatorial plane CL.

For example, in the configuration in FIG. 3, the first and secondinclined lug grooves 321A, 321B are main grooves and each have a groovedepth equivalent to that of each of the circumferential main grooves 2A,2B. In addition, both the first and second inclined lug grooves 321A,321B extend from the first and second circumferential main grooves 2A,2B to a position where the inclined lug grooves intersect the tireequatorial plane CL. Additionally, the inclined lug groove 321A, 321Bincludes a widened portion (reference sign is omitted in drawings)between the terminating end portion of the inclined lug groove and thetire equatorial plane CL.

Additionally, in FIG. 3, a distance D1 from the tire equatorial plane CLto the terminating end portion of each of the first and second inclinedlug grooves 321A, 321B has a relationship with the tire ground contactwidth TW represented by 0≤D1/TW≤0.20. Thus, the terminating end portionsof the inclined lug grooves 321A, 321B are appropriately positioned,improving the tire traction characteristics of the tire.

In the configuration illustrated in FIG. 3, both the first and secondinclined lug grooves 321A, 321B extend in the tire lateral directionbeyond the tire equatorial plane CL, and thus overlap each other.However, no such limitation is intended, and one or both of the inclinedlug grooves 321A, 321B may terminate without intersecting the tireequatorial plane CL (not illustrated). The inclined lug grooves 321A,321B may terminate without overlapping each other as viewed in the tirecircumferential direction or in the tire lateral direction (notillustrated).

The first lateral groove 322A connects the first inclined lug groove321A with the second circumferential main groove 2B. The second lateralgroove 322B connects the second inclined lug groove 321B with the firstcircumferential main groove 2A. Additionally, the single lateral groove322A, 322B opens with respect to the set of the inclined lug groove321A, 321B and the circumferential main groove 2B, 2A.

Additionally, each of the first and second lateral grooves 322A, 322Bhas a groove width of 4.0 mm or more and 20 mm or less and a groovedepth of 6.0 mm or more and 17 mm or less. In the configuration of FIG.3, as illustrated in FIG. 4, each of the first and second lateralgrooves 322A, 322B has a smaller groove width and a smaller groove depththan each of the circumferential main grooves 2A, 2B and each of theinclined lug grooves 321A, 321B. Additionally, a maximum groove depth H2of the lateral groove 322A, 322B preferably has a relationship with agroove depth H1e at the terminating end portion of the inclined luggroove 321A, 321B represented by 0.70≤H2/H1e≤0.90 and more preferably by0.75≤H2/H1e≤0.85.

In the configuration described above, the maximum groove depth H2 of thelateral groove 322A, 322B is shallower than the groove depth H1e of theterminating end portion of the inclined lug groove 321A, 321B, thusensuring an effect that holds back a flow path (that is, the lateralgroove 322A, 322B) from the inclined lug groove 321A, 321B to thecircumferential main groove 2B, 2A. Accordingly, the terminating endportion of the inclined lug groove 321A, 321B has an increased soilcolumn shear force, further improving the mud performance of the tire.Additionally, a raised bottom effect of the lateral groove 322A, 322Bincreases the rigidity of the center blocks 41A to 42B, improving thewear resistance performance of the tire.

Additionally, an inclination angle θ2 of each of the first and secondlateral grooves 322A, 322B with respect to the tire circumferentialdirection is preferably in the range of 80 deg.≤θ2≤120 deg. and morepreferably in the range of 85 deg.≤θ2≤100 deg. Thus, the first andsecond lateral grooves 322A, 322B are substantially orthogonal to thetire circumferential direction. The inclination angles θ2 of the lateralgrooves 322A, 322B are measured as angles formed between the tirecircumferential direction and a straight line extending through the leftand right opening portions of the inclined lug grooves 321A, 321Bopening to the circumferential main grooves 2A, 2B.

Additionally, in FIG. 3, a crossing angle α of each of the first andsecond lateral grooves 322A, 322B with respect to the corresponding oneof the second and first inclined lug grooves 321A, 321B is preferably inthe range of 30 deg.≤α≤75 deg. and more preferably in the range of 40deg.≤α≤60 deg.

The crossing angle α is measured as an angle formed between an extensionline of the groove center line of the lateral groove 322A, 322B and thegroove center line of the inclined lug groove 321A, 321B.

In the configuration described above, the lateral groove 322A, 322Bconnecting the circumferential main groove 2A, 2B with the inclined luggroove 321A, 321B opens laterally at an angle of 30 deg. or morerelative to the inclined lug groove 321A, 321B. Thus, a groove unit fromthe inclined lug groove 321A, 321B to the circumferential main groove2A, 2B via the lateral groove 322A, 322B has an L- or T-bent shape.Thus, the terminating end portion of the inclined lug groove 321A, 321Bhas an increased soil column shear force, improving the tractioncharacteristics of the tire.

In FIG. 3, a distance D12 to the tire equatorial plane CL from theintersection point between the groove center line of each of the secondand first inclined lug grooves 321A, 321B and the groove center line ofthe corresponding one of the first and second lateral grooves 322A, 322Bpreferably has a relationship with the tire ground contact width TW (seeFIG. 2) represented by 0≤D12/TW≤0.20. For example, in the configurationof FIG. 3, the lateral grooves 322A, 322B are connected to the inclinedlug grooves 321A, 321B in the region between the terminating endportions of the inclined lug grooves 321A, 321B and the tire equatorialplane CL.

The opening position of the lateral grooves 322A, 322B is defined as themidpoint of the measurement points of the opening width of the first andsecond lateral grooves 322A, 322B with respect to the inclined luggrooves 321A, 321B.

In FIG. 3, an extension length D2 of each of the first and secondlateral grooves 322A, 322B in the tire lateral direction has arelationship with a maximum ground contact width Wb2 of the center landportion 32 represented by 0.10≤D2/Wb2≤0.30.

Additionally, in FIG. 3, a distance L2, in the tire circumferentialdirection, of the opening position of each of the first and secondlateral grooves 322A, 322B with respect to the corresponding one of thesecond and first inclined lug grooves 321A, 321B preferably has arelationship with a pitch length P2 of the center block 41A representedby 0≤L2/P2≤0.30.

Each of the first and second auxiliary grooves 323A, 323B connects thefirst inclined lug grooves 321A with the second inclined lug grooves321B, which are adjacent to each other. Additionally, the first andsecond auxiliary grooves 323A, 323B are disposed alternately in the tirecircumferential direction.

Additionally, each of the first and second auxiliary grooves 323A, 323Bhas a groove width of 2.0 mm or more and 23 mm or less and a groovedepth of 6.0 mm or more and 17 mm or less. In the configuration of FIG.3, each of the first and second auxiliary grooves 323A, 323B has asmaller groove depth than each of the circumferential main grooves 2A,2B and each of the inclined lug grooves 321A, 321B. Specifically, amaximum groove depth H3 (not illustrated) of each of the first andsecond auxiliary grooves 323A, 323B preferably has a relationship withthe groove depth H1 (see FIG. 4) of each of the first and secondinclined lug grooves 321A, 321B represented by 0.70≤H3/H1≤0.90 and morepreferably by 0.75≤H3/H1≤0.85.

In addition, inclination angles θ3A, 03B of the first and secondauxiliary grooves 323A, 323B are preferably in the range of 10deg.≤θ3A≤30 deg. and 30 deg.≤θ3B≤85 deg. and more preferably in therange of 15 deg.≤θ3A≤25 deg. and 40 deg.≤θ3B≤80 deg. Additionally, theinclination angle θ3A of the first auxiliary groove 323A with respect tothe tire circumferential direction is smaller than the inclination angleθ3B of the second auxiliary groove 323B. Specifically, a differencebetween the inclination angles θ3A and 03B is preferably in the range of15 deg.≤θ3A-θ3B.

The inclination angles θ3A, 03B of the auxiliary grooves 323A, 323B aremeasured as angles formed between the tire circumferential direction anda straight line extending through the left and right opening portions ofthe inclined lug grooves 321A, 321B.

For example, in the configuration in FIG. 3, the first and secondauxiliary grooves 323A, 323B are disposed on the tire equatorial planeCL and define the center blocks 41A to 42B. Additionally, each of thefirst auxiliary grooves 323A defines the first center blocks 41A, 41B,described below, and each of the second auxiliary grooves 323B definesthe second center blocks 42A, 42B, described below. Additionally, thefirst and second auxiliary grooves 323A, 323B have different inclinationangles θ3A, θ3B and are inclined in the same direction with respect tothe tire circumferential direction.

Center Block

FIGS. 5 and 6 are explanatory diagrams illustrating center blocks of thecenter land portion illustrated in FIG. 3. In these drawings, FIG. 5illustrates a pair of first center blocks 41A, 41B, and FIG. 6illustrates a pair of center blocks 42A, 42B.

As illustrated in FIG. 2, the center blocks 41A, 41B, 42A, 42B aredefined into the grooves described above, that is, the first and secondcircumferential main grooves 2A, the first and second inclined luggrooves 321A, 321B, the first and second lateral grooves 322A, 322B, andthe first and second auxiliary grooves 323A, 323B.

Here, of the plurality of center blocks 41A, 41B, 42A, 42B, the centerblocks 41A, 41B disposed on an extension line of the groove center linesof the first and second inclined lug grooves 321A, 321B are defined asfirst center blocks. Additionally, the center blocks 42A, 42B disposedbetween the first and second inclined lug grooves 321A, 321B are definedas second center blocks. In the configuration of FIG. 2, the pair ofcenter blocks 41A, 41B are defined as first center blocks, and the pairof center blocks 42A, 42B are defined as second center blocks.

In the configuration in FIG. 2, block units (reference sign omitted indrawings) each including a set of the pair of first center blocks 41A,41B and the pair of second center blocks 42A, 42B are arrangedrepeatedly in the tire circumferential direction to form a block row ofthe center land portion 32. Additionally, as illustrated in FIG. 3, thefirst center block 41A and the second center block 42B, located on theleft side of FIG. 3, are disposed in a row in the tire circumferentialdirection with edge portions on the first circumferential main groove 2Aside aligned with each other. In addition, the first center block 41Band the second center block 42A, located on the right side of FIG. 3,are disposed in a row in the tire circumferential direction along thesecond circumferential main groove 2B with edge portions on the tirelateral direction outer side aligned with each other. Additionally, theleft and right first center blocks 41A, 41B are disposed offset fromeach other in the tire circumferential direction, and the left and rightsecond center blocks 42A, 42B are disposed offset from each other in thetire circumferential direction.

Note that, in the configuration in FIG. 2, one block unit includes thepair of first center blocks 41A, 41B and the pair of second centerblocks 42A, 42B as described above. However, no such limitation isintended, and one block unit may include a pair of first center blocksand two or more (for example, three) second center blocks (notillustrated). Even in this case, the first center blocks and the secondcenter blocks are alternately arranged in the tire circumferentialdirection to form a block row of the center land portion 32.

Additionally, in the configuration in FIG. 3, each of the first andsecond lateral grooves 322A, 322B has the inclination angle θ2substantially orthogonal to the tire circumferential direction asdescribed above. Thus, the center blocks 41A to 42B defined by thelateral grooves 322A, 322B include respective edge portionssubstantially orthogonal to the tire circumferential direction. Thisensures edge components of the center blocks 41A to 42B, improving themud performance of the tire.

Additionally, in FIGS. 5 and 6, a maximum length Lb1 of the centerblocks 41A to 42B in the tire circumferential direction and a maximumwidth Lb2 of the center blocks 41A to 42B in the tire lateral directionhave a relationship of 0.70≤Lb2/Lb1≤1.10. In addition, the maximumlength Lb1 of the center blocks 41A to 42B preferably has a relationshipwith the pitch length P2 (see FIG. 3) of the center block 41Arepresented by 0.40≤Lb1/P2≤0.70. Additionally, the maximum width Lb2 ofthe center blocks 41A to 42B preferably has a relationship with the tireground contact width TW (see FIG. 2) represented by 0.10≤Lb2/TW≤0.50 andmore preferably by 0.20≤Lb2/TW≤0.40.

The maximum length Lb1 and the maximum width Lb2 of the center blocks41A to 42B are measured on the contact surface between the land portionand a flat plate, with the tire mounted on a specified rim, inflated tothe specified internal pressure, and placed perpendicularly to the flatplate in a stationary state and loaded with a load corresponding to thespecified load.

Notch Portion of Center Block

FIG. 7 is an enlarged view illustrating a notch portion illustrated inFIG. 5.

In FIG. 3, the first center blocks 41A, 41B are disposed on theextension line of the first and second inclined lug grooves 321A, 321B.Edge portions of the first center blocks 41A, 41B each include a firstnotch portion 51.

The first notch portion 51 is a groove-shaped recess portion opening inthe block road contact surface. The first notch portion 51 is formed inan edge portion of the first center block 41A, 41B and opens to aterminating end portion of the first or second inclined lug groove 321A,321B.

For example, in the configuration of FIG. 3, the pair of first centerblocks 41A, 41B each include the first notch portion 51, which is Ushaped, and the first notch portions 51 are disposed on the extensionline of the groove center lines of the first and second inclined luggrooves 321A, 321B to extend the terminating end portions of theinclined lug grooves 321A, 321B. Additionally, the first notch portion51 opens at connecting portions between the inclined lug grooves 321A,321B and the lateral grooves 322A, 322B.

In the configuration described above, the edge portions of the firstcenter blocks 41A, 41B each include the first notch portion 51 openingat the corresponding one of the terminating end portions of the inclinedlug grooves 321A, 321B, thus increasing the soil column shear force toimprove a mud discharge function. Thus, the mud performance of the tireis improved.

Additionally, an opening area Sc of the first notch portion 51 withrespect to an area Sb of the road contact surface of each of the firstcenter blocks 41A, 41B is preferably in the range of 0.003≤Sc/Sb≤0.030and more preferably in the range of 0.004≤Sc/Sb≤0.020.

As illustrated in FIG. 7, the opening area Sc of the first notch portion51 is calculated as the area of a closed region bounded by a normal lineextended from an opening end of the first notch portion 51 on thelateral groove 322A (322B) side, toward the other wall surface, in aplan view of the first center block 41A (41B).

The area Sb of the road contact surface of the block is calculated asthe area of a region of the block enclosed by a contour line in a treadplan view.

In FIG. 4, a maximum depth Hc1 of the first notch portion 51 preferablyhas a relationship with the groove depth H1e of the terminating endportion of each of the inclined lug grooves 321A, 321B represented by0.80≤Hc1/H1e≤1.00.

Additionally, in FIG. 3, the second center blocks 42A, 42B are disposedbetween the first and second inclined lug grooves 321A, 321B asdescribed above. Edge portions of the second center blocks 42A, 42B eachinclude a second notch portion 52.

The second notch portion 52 is a groove-shaped recess portion that opensin the block road contact surface. The second notch portion 52 is formedat an edge portion of the second center block 42A, 42B and opens to thefirst or second circumferential main groove 2A, 2B.

For example, in the configuration of FIG. 3, the pair of second centerblocks 42A, 42B each include the second notch portion 52, which is Vshaped, and the second notch portions 52 respectively open at maximumamplitude positions of the first and second circumferential main grooves2A, 2B. Additionally, the second notch portion 52 opens at theconnecting portion between the circumferential main grooves 2A, 2B andthe lateral grooves 322A, 322B. Thus, the mud performance of the tire isimproved.

Additionally, a maximum depth Hc2 (not illustrated) of the second notchportion 52 preferably has a relationship with the groove depth Hg (seeFIG. 4) of each of the circumferential main grooves 2A, 2B (see FIG. 4)represented by 0.80≤Hc2/Hg≤1.00.

Additionally, as illustrated in FIGS. 5 and 6, each of the center blocks41A to 42B includes a through sipe 53, a pair of narrow grooves 54A,54B, and a plurality of closed sipes 55.

The through sipes 53 extend through the center blocks 41A to 42B andopen at left and right edge portions of the center blocks 41A to 42B.

The narrow grooves 54A, 54B extend along the through sipes 53. Eachnarrow groove 54A, 54B opens, at one end portion, to an edge portion ofa corresponding one of the center blocks 41A to 42B and terminates, atthe other end portion, within the corresponding one of the center blocks41A to 42B. Additionally, a maximum groove depth Hs (not illustrated) ofeach narrow groove 54A, 54B has a relationship with the groove depth Hgof each circumferential main groove 2A, 2B (see FIG. 4) represented by0.60≤Hs/Hg≤0.90.

Note that instead of the narrow grooves 54A, 54B, chamfered portions orwhat is called chamfered sipes may be formed that extend along thethrough sipes 53 and that open to the road contact surfaces of thecenter blocks 41A to 42B (not illustrated).

The closed sipes 55 terminate within the center blocks 41A to 42B.Additionally, a plurality of the closed sipes 55 are each disposed inone of the left and right regions of the center blocks 41A to 42Bdefined by the through sipes 53.

The sipes are cuts formed in the tread contact surface and each have asipe width of less than 1.5 mm and a sipe depth of 2.0 mm or more. Thus,the sipes close when the tire comes into contact with the ground.

The sipe width is measured as the maximum opening width of the sipe onthe tread contact surface, with the tire mounted on a specified rim andinflated to the specified internal pressure and in an unloaded state.

The sipe depth is measured as a distance from the tread contact surfaceto the maximum depth position of the sipe, with the tire is mounted on aspecified rim and inflated to the specified internal pressure and in anunloaded state. Additionally, in a configuration in which a sipepartially includes a recess/protrusion portion on the groove bottom, thesipe depth is measured excluding this portion.

Note that in the configuration in FIG. 6, each of the second centerblocks 42A, 42B includes a chamfered portion 56 at an acute corner.

Effects

As described above, the pneumatic tire 1 includes the first and secondcircumferential main grooves 2A, 2B extending in the tirecircumferential direction, and the pair of shoulder land portions 31A,31B and the one row of the center land portion 32 defined by the firstand second circumferential main grooves 2A, 2B (see FIG. 2).Additionally, the center land portion includes: the plurality of firstinclined lug grooves 321A each extending at an incline with respect tothe tire circumferential direction and opening, at one end portion, tothe first circumferential main groove 2A and terminating, at the otherend portion, within the center land portion 32; the plurality of secondinclined lug grooves 321B each extending at an incline in the samedirection as the first inclined lug grooves 321A and opening, at one endportion, to the second circumferential main groove 2B and terminating,at the other end portion, within the center land portion 32; theplurality of first lateral grooves 322A each connecting the firstinclined lug groove 321A with the second circumferential main groove 2B;the plurality of second lateral grooves 322B each connecting the secondinclined lug groove 321B and the first circumferential main groove 2A;the plurality of auxiliary grooves 323A, 323B each connecting the firstinclined lug groove 321A with the second inclined lug groove 321Badjacent to each other; and the plurality of center blocks 41A, 41B,42A, 42B defined by the grooves (see FIG. 3). Additionally, the maximumgroove depth H1 of the first (and second) inclined lug groove 321A(321B) over the entire area from the opening to the first (and second)circumferential main groove 2A (2B) to the terminating end portionwithin the center land portion 32 has a relationship with the maximumgroove depth Hg of the first (and second) circumferential main groove 2A(2B) represented by 0.80≤H1/Hg≤1.00 (see FIG. 4). Additionally, themaximum groove depth H2 of the first (and second) lateral groove 322A(322B) has a relationship with the groove depth H1e at the terminatingend portion of the first (and second) inclined lug groove 321A (321B)represented by 0.70≤H2/H1≤0.90.

In the configuration as described above, (1) each of the inclined luggrooves 321A, 321B terminates within the center land portion 32 withoutextending through the center land portion 32. Thus, compared to aconfiguration in which the inclined lug groove extends through thecenter land portion (not illustrated), a soil column shear force duringtraveling on a snowy road is increased. This has the advantage ofimproving the traction characteristics of the tire, improving the mudperformance the tire. Additionally, advantageously, the rigidity of thecenter blocks 41A to 42B is increased to improve the wear resistanceperformance of the tire.

Additionally, (2) the maximum groove depth H2 of the lateral groove322A, 322B is shallower than the groove depth H1e of the terminating endportion of the inclined lug groove 321A, 321B, thus ensuring an effectthat holds back a flow path (that is, the lateral groove 322A, 322B)from the inclined lug groove 321A, 321B to the circumferential maingroove 2A, 2B. Thus, advantageously, the terminating end portion of theinclined lug groove 321A, 321B has an increased soil column shear force,further improving the mud performance of the tire. Additionally,advantageously, a raised bottom effect of the lateral groove 322A, 322Bincreases the rigidity of the center blocks 41A to 42B, improving thewear resistance performance of the tire.

Additionally, in the pneumatic tire 1, the plurality of center blocks41A to 42B include the pair of first center blocks 41A, 41B disposedadjacent in the tire lateral direction and the two or more second centerblocks 42A, 42B disposed adjacent in the tire lateral direction, thefirst center blocks 41A, 41B and the second center blocks 42A, 42B beingalternately arranged in the tire circumferential direction (see FIG. 3).Additionally, the pair of first center blocks 41A, 41B are disposed onthe extension line of the first and second inclined lug grooves 321A,321B. Thus, advantageously, the center blocks 41A to 42B areappropriately disposed with respect to the inclined lug grooves 321A,321B, improving the mud performance of the tire.

Additionally, in the pneumatic tire 1, the maximum width Lb2 (see FIGS.5 and 6) of the center blocks 41A to 42B has a relationship with thetire ground contact width TW represented by 0.10≤Lb2/TW≤0.50.Advantageously, the above-described lower limit appropriately ensuresthe maximum width Lb2 of the center blocks 41A to 42B, suppressinguneven wear of the blocks. In addition, advantageously, theabove-described upper limit suppresses a reduction in groove area ratiocaused by an excessive amount of blocks, ensuring the mud performance ofthe tire.

Additionally, in the pneumatic tire 1, the maximum ground contact widthWb2 of the center land portion 32 with respect to the tire groundcontact width TW is in the range of 0.30≤Wb2/TW≤0.60 (see FIG. 2). Thishas the advantage of appropriately setting the width Wb2 of the centerland portion 32.

Additionally, in the pneumatic tire 1, the inclination angle θ1 of thefirst (and second) inclined lug groove 321A (321B) in the tireequatorial plane CL is in the range of 25 deg.≤θ1≤70 [deg]. This has theadvantage of making the inclination angle θ1 of the inclined lug groove321A (321B) appropriate, thus ensuring the traction characteristics ofthe tire.

Additionally, in the pneumatic tire 1, the distance D1 from the tireequatorial plane CL to the terminating end portion of the first (andsecond) inclined lug groove 321A (321B) has a relationship with the tireground contact with TW represented by 0≤D1/TW≤0.20. Thus, theterminating end portion of the inclined lug groove 321A (321B) isappropriately positioned, advantageously improving the tire tractioncharacteristics of the tire.

Additionally, in the pneumatic tire 1A, the inclination angle θ2 of thefirst (and second) lateral groove 322A (322B) with respect to the tirecircumferential direction is in the range of 80 deg.≤θ2≤120 deg. (seeFIG. 3). In such a configuration, advantageously, the lateral groove322A (322B) is substantially orthogonal to the tire circumferentialdirection, advantageously improving the traction characteristics of thetire.

Additionally, in the pneumatic tire 1, the crossing angle α of the first(and second) lateral groove 322A (322B) with respect to the first (andsecond) inclined lug groove 321A (321B) is in the range of 30 deg.≤α≤75deg. (see FIG. 3). In the configuration as described above, the lateralgroove 322A (322B) connecting the inclined lug groove 321A (321B) withthe circumferential main groove 2B (2A) opens laterally at an angle of30 deg. or more relative to the inclined lug groove 321A (321B). Thus, agroove unit from the inclined lug groove 321A (321B) to thecircumferential main groove 2B (2A) via the lateral groove 322A (322B)has an L-bent shape. Thus, advantageously, the terminating end portionof the inclined lug groove 321A (321B) has an increased soil columnshear force, improving the traction characteristics of the tire.

Additionally, in the pneumatic tire 1, the distance D12 to the tireequatorial plane CL from the intersection point between the groovecenter line of each of the first and second inclined lug grooves 321A,321B and the groove center line of the corresponding one of the firstand second lateral grooves 322A, 322B has a relationship with the tireground contact width TW represented by 0≤D12/TW≤0.20. This makes theopening positions of the first and second lateral grooves 322A, 322Bwith respect to the inclined lug grooves 321A, 321B appropriate,advantageously improving the traction characteristics of the tire.

Additionally, in the pneumatic tire 1, the extension length D2 of thefirst (and second) lateral groove 322A (322B) in the tire lateraldirection has a relationship with the maximum ground contact width Wb2of the center land portion 32 represented by 0.10≤D2/Wb2≤0.30 (see FIG.3). This has the advantage of making the extension length D2 of thelateral grooves 322A (322B) appropriate.

Additionally, in the pneumatic tire 1, the maximum groove depth H3 ofeach of the auxiliary grooves 323A, 323B (not illustrated) has arelationship with the groove depth H1 (see FIG. 4) of the first (andsecond) inclined lug groove 321A (321B) represented by 0.70≤H3/H1≤0.90.Accordingly, the inclined lug groove 321A (321B) has an increased soilcolumn shear force, further advantageously improving the mud performanceof the tire. Additionally, the raised bottom effect of the auxiliarygrooves 323A, 323B increases the rigidity of the center blocks 41A to42B, improving the wear resistance performance of the tire.

Additionally, in the pneumatic tire 1, the edge portion of the centerblock 41A (41B) included in the plurality of center blocks 41A to 42Band disposed on the extension line of the first (and second) inclinedlug groove 321A (321B) includes the notch portion 51 opening at theterminating end portion of the first inclined lug groove 321A (or thesecond inclined lug groove 321B). This has the advantage of improvingthe mud performance of the tire.

Additionally, in the pneumatic tire 1, the opening area Sc of the notchportion 51 with respect to the area Sb of the road contact surface ofthe center blocks 41A, 41B is in the range of 0.01≤Sc/Sb≤0.05. The lowerlimit described above has the advantage of ensuring an effect thatimproves soil columnar shear force by the notch portion 51. In addition,advantageously, the upper limit described above suppresses a reductionin block rigidity caused by an excessive amount of blocks, ensuring thewear resistance performance of the tire.

Additionally, in the pneumatic tire 1, the first and secondcircumferential main grooves 2A, 2B each have a zigzag shape with anamplitude in the tire lateral direction (see FIG. 2). Additionally, thepair of shoulder land portions 31A, 31B and the center land portion 32are disposed overlapping each other in the tire circumferentialdirection. This has the advantage of ensuring traction characteristicson mud roads, thus ensuring the mud performance of the tire.

Example

FIGS. 8A-8C include a table showing results of performance tests ofpneumatic tires according to embodiments of the technology.

In the performance tests, a plurality of different test tires wereevaluated for (1) mud performance and (2) wear resistance performance.Additionally, a test tire having a tire size of LT265/70R17 121Q isassembled on a rim having a rim size of 17×8 J, and the test tire isinflated to an internal pressure of 450 kPa and loaded with a loadspecified by JATMA. Additionally, the test tires are mounted on allwheels of an LT pickup vehicle used as a test vehicle.

(1) In the evaluation of mud performance, the test vehicle is driven ona predetermined mud road, and a test driver performs sensory evaluationregarding traction characteristics. Results of the evaluation areexpressed as index values and evaluated with the Conventional Examplebeing assigned as the reference (100). In this evaluation, larger valuesare preferable.

(2) In the evaluation of wear resistance performance, after the testvehicle travels 8000 km on a predetermined offload course, the degree ofwear is observed and an index evaluation is performed. Results of theevaluation are expressed as index values and evaluated with theConventional Example being assigned as the reference (100). In thisevaluation, larger values are preferable.

The test tires according to Examples have the configuration in FIGS. 1and 2 and include the pair of circumferential main grooves 2A, 2B havinga zigzag shape, the pair of shoulder land portions 31A, 31B, and thesingle center land portion 32. Additionally, the tire ground contactwidth TW is 222 mm, and the maximum ground contact width Wb2 of thecenter land portion 32 is 108 mm. In addition, each of thecircumferential main grooves 2A, 2B has a groove width of 14.0 mm and agroove depth Hg of 14.6 mm. Additionally, each of the inclined luggrooves 321A, 321B has a groove width of 9.7 mm, and each of the lateralgrooves 322A, 322B and the auxiliary grooves 323A, 323B has a groovewidth of 6.0 mm.

The test tires according to Conventional Example correspond to the testtires according to Example 1 in which the inclined lug grooves 321A,321B extend through the center land portion 32 and open to the left andright circumferential main grooves 2A, 2B. Thus, the center land portion32 does not include the lateral grooves 322A, 322B (or each of thelateral grooves 322A, 322B has the same groove depth as that of each ofthe inclined lug grooves 321A, 321B, thus forming a portion of each ofthe inclined lug grooves 321A, 321B).

As can be seen from the test results, the mud performance and wearresistance performance of the tire are improved in the test tiresaccording to Examples.

1. A pneumatic tire comprising: first and second circumferential maingrooves extending in a tire circumferential direction; and a pair ofshoulder land portions and one row of a center land portion defined bythe first and second circumferential main grooves, the center landportion comprising: a first inclined lug groove extending at an inclinewith respect to the tire circumferential direction and opening, at oneend portion, to the first circumferential main groove and terminating,at another end portion, within the center land portion; a secondinclined lug groove extending at an incline in a direction identical toa direction of the first inclined lug groove and opening, at one endportion, to the second circumferential main groove and terminating, atanother end portion, within the center land portion; a first lateralgroove connecting the first inclined lug groove with the secondcircumferential main groove; a second lateral groove connecting thesecond inclined lug groove and the first circumferential main groove;first and second auxiliary grooves connecting the first inclined luggroove with the second inclined lug groove adjacent to each other; and aplurality of center block defined by the grooves, a groove depth H1 ofthe first inclined lug groove over an entire region from an openingportion to the first circumferential main groove to a terminating endportion within the center land portion having a relationship with amaximum groove depth Hg of the first circumferential main grooverepresented by 0.80≤H1/Hg≤1.00, and a maximum groove depth H2 of thefirst lateral groove having a relationship with a groove depth H1e atthe terminating end portion of the first inclined lug groove representedby 0.70≤H2/H1e≤0.90.
 2. The pneumatic tire according to claim 1, whereinthe plurality of center blocks include a pair of first center blocksdisposed adjacent in a tire lateral direction and two or more secondcenter blocks disposed adjacent in the tire lateral direction, the firstcenter blocks and the second center blocks being alternately arranged inthe tire circumferential direction, and the pair of first center blocksare disposed on an extension line of the first and second inclined luggrooves.
 3. The pneumatic tire according to claim 1, wherein a maximumwidth Lb2 of the first center blocks has a relationship with a tireground contact width TW represented by 0.10≤Lb2/TW≤0.50.
 4. Thepneumatic tire according to claim 1, wherein a maximum ground contactwidth Wb2 of the center land portion with respect to the tire groundcontact width TW is in a range of 0.30≤Wb2/TW≤0.60.
 5. The pneumatictire according to claim 4, wherein an inclination angle θ1 of the firstinclined lug groove with respect to a tire equatorial plane is in arange of 25 deg.≤θ1≤70 deg.
 6. The pneumatic tire according to claim 1,wherein a distance D1 from the tire equatorial plane to the terminatingend portion of the first inclined lug groove has a relationship with thetire ground contact with TW represented by 0≤D1/TW≤0.20.
 7. Thepneumatic tire according to claim 1, wherein an inclination angle θ2 ofthe first lateral groove with respect to the tire circumferentialdirection is in a range of 80 deg.≤θ2≤120 deg.
 8. The pneumatic tireaccording to claim 1, wherein a crossing angle α of the first lateralgroove with respect to the first inclined lug groove is in a range of 30deg.≤α≤75 deg.
 9. The pneumatic tire according to claim 1, wherein adistance D12 to the tire equatorial plane from an intersection pointbetween the groove center line of the first inclined lug groove and thefirst lateral groove has a relationship with the tire ground contactwidth TW represented by 0≤D12/TW≤0.20.
 10. The pneumatic tire accordingto claim 1, wherein an extension length D2 of the first lateral groovein the tire lateral direction has a relationship with the maximum groundcontact width Wb2 of the center land portion represented by0.10≤D2/Wb2≤0.30.
 11. The pneumatic tire according to claim 1, wherein amaximum groove depth H3 of the auxiliary groove has a relationship withthe groove depth H1 of the first inclined lug groove represented by0.70≤H3/H1≤0.90.
 12. The pneumatic tire according to claim 11, whereinan opening area Sc of the notch portion with respect to an area Sb of aroad contact surface of the center block is in a range of0.01≤Sc/Sb≤0.05.
 13. The pneumatic tire according to claim 1, wherein anedge portion of the center block included in the plurality of centerblocks and disposed on an extension line of the first inclined luggroove includes a notch portion opening at a terminating end portion ofthe first inclined lug groove.
 14. The pneumatic tire according to claim12, wherein an opening area Sc of the notch portion with respect to anarea Sb of a road contact surface of the center block is in a range of0.01≤Sc/Sb≤0.05.
 15. The pneumatic tire according to claim 1, whereineach of the first and second circumferential main grooves has a zigzagshape with an amplitude in the tire lateral direction, and the pair ofshoulder land portions and the center land portion are disposedoverlapping each other as viewed in the tire circumferential direction.